1. Technical Field
The invention is related to airborne acoustic sensors of the type including a microphone on an airborne vehicle such as a glider, and more particularly to such sensors having low noise characteristics.
2. Background Art
Airborne acoustic sensors or microphones are limited in their performance because of air turbulence around the sensor which induces noise. Some turbulence will always be present which creates great noise picked up by the microphone.
Static pressure probes which are virtually insensitive to pitch, yaw and speed have been disclosed by A. M. O. Smith and A. B. Bauer, "Static-pressure probes that are theoretically insensitive to pitch, yaw and Mach number," J. Fluid Mechanics, (1970), vol. 44, part 3, pages 513-528, in which the housing has a clover-leaf cross-sectional shape with four concave indentations, each one of four radial ports in the housing nested in a respective one of the four indentations. As disclosed in that publication, the principal advantage is that the static pressure at the intersection of the four radial ports (at the center of the housing) is insensitive to cross-wind velocities. If the four radial ports are located at a longitudinal point along the housing at which the pressure coefficient is zero (that is, where the pressure at the housing surface equals the ambient atmospheric pressure), then a theoretically perfect measurement of static pressure is obtained at the intersection of the four microphone 3 ports. However, static pressure probes are useful for measuring speed, but have nothing to do with sensing sound waves or acoustic signals.